The introduction of chemical warfare during the First World War was a major event in the history of military technology. It not only posed an unusual challenge to military thinking of the day, which was largely conventional and wholly unfamiliar with science, it also created a heated moral controversy surrounding the new weapon that did not discriminate between soldiers and civilians. This study, based on a previously unavailable range of archival material and statistical data, explores the military role of chemical warfare as well as its effects on people, industries and administration on both sides. The book also fully examines the complex issues raised by this new technology, which were debated endlessly between the wars and have led to recent agreements among the powers to curb their use of chemical or biological warfare. This study was planned in close cooperation with Sir Harold Hartley, who became head of British chemical warfare in 1918.